While size of trap is relevant, first be sure your traps are "strong" enough for the trashing a dog is goin to put on them. As far as size of trap, trappers use 1.5s up to 3s and even bigger for coyotes. Myself, I run mb-550s with the occasional "cheaper" trap when setting close to roads/ people; #2s will work just fine.
Dirt hole sets can be deadly, especially on fox. But make sure you learn how to use flat sets/ scent posts/ trench sets/ etc.. They all have their place on a productive line. As far as lures, try different ones and keep a log book of what lure/ bait combo you used at which set. This will help you key in on what works better in your area.
The most important thing I can stress to you right now is scent control and trap placement at your set.
...by-god Woodrow, it's been quite a party ain't it.